The present invention relates, in general, to thermal detection techniques and, in particular, to a new and useful method and apparatus for determining the exposure of a component to a selected temperature above an ambient, by examining the component for the presence or absence of a coupon which has previously been bonded to the component utilizing a bonding agent which fails at the selected temperature.
Heavy oil and tar sands represent huge untapped resources of liquid hydrocarbons which will be produced in increasing quantities to help supplement declining production of conventional crude oil. These deposits must, however, be heated to reduce the oil viscosity before it will flow to the producing wells in economical quantities. The dominant method of heating is by injection of surface generated steam in either a continuous (steam flood) or intermittent (steam stimulation or "huff and puff") mode.
When steam is injected down long injection pipes or "strings", a significant amount of thermal energy is lost to the rock overburden (500 to 700 feet) which covers the oil deposit. In the initial steam injection projects, the price of oil did not justify the prevention of this heat loss, but now with the price of oil at $30.00 or more a barrel, insulation systems for the well injection pipe become economically justified.
Several methods are known for determining the exposure of a component to an excess selected temperature which is indicative of insulation failure. Such methods include the real time or service monitoring of surface temperature using thermocouples, thermistors, thermometers, optical pyrometers or infrared cameras.
A system of monitoring the input and output fluid temperatures may also be utilized for determining the integrity of the insulation, where the component is designed for conveying a fluid. Additionally, a measurement of power output verses fuel consumption, i.e., efficiency, gives an indication of the state of the insulation since, a degraded insulation would reduce efficiency.
In all of the aforementioned techniques, once the component has cooled to ambient temperature, the evidence of thermal failure is no longer present. The techniques must be exercised during real time and thus are limited to cases where real time monitoring is possible and practical.
Off-line Thermal Testing Techniques are also known which either directly establish the integrity of the insulation or infer this integrity. The component is removed from service for testing.
According to one technique, an induced heat flow using an induction heater is monitored by an infrared camera or other temperature sensing equipment. Alternatively, the component can be placed into a test loop in which thermal efficiency is measured.
Thermal failure can be inferred in an off-line situation by observing the conditions of the component or some part thereof, which has previously been exposed to overheating. Visual inspection may determine severe degradation, for example, warping or melting of the component due to overheating. Discoloration of the normal surface appearance is also a clue to thermal failure. This discoloration may be indicative of a change in tempering or the like. A paint that permanently changes color when exposed to a particular temperature can be applied to such things as storage tanks in chemical factories. The usefulness of such a paint for rugged extreme environments has not been established, however, in particular for oil well environments where steam is injected into a well to extract otherwise "frozen" oil supplies.
It is known to utilize injected steam to extract such oil supplies. Such steam is injected into a well using an insulated steam injection tube which, in known fashion, comprises inner and outer coaxial tubes defining between them an annular space which is provided with insulation means, such as thermal insulation and evacuation of the space to obtain a vacuum. The use of insulation between the coaxial tubes is disclosed, for example, in U.S. Pat. No. 3,574,357 to Alexandru et al and U.S. Pat. No. 3,478,783 to Doyle.